Every power transformer above 72.5 kV gets an IVPD test before it ships. The test takes more than an hour, costs the manufacturer significant test bay time, and is the final dielectric test in the sequence. Why? Because partial discharge is what kills transformer insulation slowly, and most other tests can’t see it. A lightning impulse test stresses… Read More »
When a power transformer arrives at site, the test report is mostly numbers. LI, LIC, SI, AV, IVW, IVPD, LTAC. Test voltages in kV. PD readings in pC. Clearances in mm. If you didn’t write the spec, you’re reading someone else’s interpretation of a standard you might not have in front of you. That standard, for most of… Read More »
If you’ve been doing motor insulation testing for any length of time, you’ve heard the standard cited a hundred times. “IEEE 43 says the PI minimum is 2.0.” “IEEE 43 requires correction to 40°C.” Most techs and engineers work from the rules without ever opening the document. That works fine until it doesn’t. Until an auditor asks where… Read More »
Every motor failure has a story. Most start the same way — insulation that gave out before the winding did. Heat, vibration, moisture, voltage spikes, chemicals. One or all of them. The question isn’t if insulation degrades. It’s how fast — and what’s driving it. This article covers the five aging stresses, what each one actually does to… Read More »
The DC hipot test is the most consequential offline test you can run on a stator winding. It applies a high DC voltage — well above operating levels — to the groundwall insulation and holds it there. If the insulation fails during the test, you know before the machine goes back into service. If it passes, you have… Read More »
Most stator failures are not sudden. They are the end point of a process that has been running for months or years — visible if you know what to look for, detectable by testing before the insulation finally fails in service. Understanding the failure mechanism behind a bad test result is the difference between cleaning a winding and… Read More »
Most people who run a Polarization Index test can tell you the formula: 10-minute IR divided by 1-minute IR. Fewer can tell you why that ratio is meaningful, where it stops being meaningful, or what a result of 1.1 on a modern epoxy-mica winding actually implies — compared to the same reading on an asphaltic machine from 1965.… Read More »
Insulation resistance testing is one of the most practical condition assessment tools in electrical maintenance. Apply DC voltage to a winding, measure the leakage current, divide one by the other — you get a number in megohms that tells you whether the insulation is clean and dry, wet and contaminated, or failing. IEEE 43-2013 is the standard that… Read More »
Choose the wrong insulation tester and you’ll either waste money on capabilities you don’t need or get stuck with equipment that can’t handle the job. Both happen often. A residential electrician buying a $3,000 5-kV tester to verify branch circuits, or an industrial maintenance team trying to test 13.8 kV motor windings with a 1 kV handheld —… Read More »
If you’ve spent any time shopping for an insulation tester, you already know the market is flooded with options. But when it comes to professional-grade instruments trusted in the field, three names keep coming up: Fluke, Megger, and Hioki. Each brand has built a serious reputation — and each takes a meaningfully different approach to what an insulation… Read More »